1. Field of the Invention
The present invention relates to an electronic desk calculator having a counter function, a verification function or a state display function.
2. Description of the Related Art
Japanese Laid-Open Patent Publication Nos. 50-11496 and 57-136270 disclose a calculator having a counter function. The counter provided in a conventional calculator counts how many time an operator key(s) is depressed to count the number of numeral units. Moreover, when a key for clearing the result of a calculation is depressed, the value stored in the counter is also disadvantageously cleared.
By inputting elements, the calculator performs a calculation based on input elements. The elements are classified into at least a numeral unit and an operator. For example, in the case where an expression "1000+500=" is to be calculated, "1000" and "500" are numeral units, and "+" and "=" are operators.
The counters disclosed in Japanese Laid-Open Patent Publication Nos. 50-11496 and 57-136270 assume counting in a calculator basically performing addition. However, the above Patent Publications show neither a counting operation in a calculator performing a calculation in accordance with a formula nor a counting operation for a specific operator key.
In a conventional technique, since a counting operation is performed at the time when the operator key is depressed, a value on the counter shows the number of operators, but not the number of numeral units. Therefore, if a user forgets the position of an input element, a method for seeking the position of the input element in the case where the numeral unit is input differs from that in the case where the operator is input. In the case where the numeral unit is input, the numeral unit obtained by adding one to the value of the counter should be searched for from elements including the numeral unit. Immediately after entering the operator, the numeral unit identical with the value of the counter should be searched for from the element.
Furthermore, In a conventional technique, in the case where the result of a calculation is cleared by a clear key, the value of the counter is also cleared. If another calculation is executed after execution of one calculation in a calculator in accordance with an expression, there arises a problem that the value of the counter is not cleared regardless of the operation of the clear key.
In a conventional technique, the number of depressions of the operator key is counted. Therefore, after depressing a wrong key, when a correct operator key is depressed in accordance with an expression so as to perform a correction, the number of actually performed calculations and the number of depressions of the operator key are different from each other. Thus, the counter does not indicate a correct value.
According to a conventional technique, in the case where a user repeatedly inputs the same operator and the same numeral unit, the repeated input of the same operator and the same numeral unit can be omitted by depressing a particular key, for example, "=". Thus, the number of calculations actually performed and the number indicated by the counter are not identical with each other.
In the case where two or more calculations are allocated to a key displaying the plurality of results of loop calculations in turn, for example, a tax key, the number of calculations and the number indicated by the counter are not identical with each other because the number of actual depressions of the key is counted.
In a conventional technique, a counter for memory counts the number of depression of a M+! key or a M-! key. However, even in the case where an expression (including an operator and a numeral unit) is input so au to simultaneously execute the expression by using the M+! key and the addition of the result thereof to the memory, the value of the counter is increased by only one. Therefore, the number of actual calculations and the number counted by the counter arm not disadvantageously not identical with each other.
In a conventional technique, the number of counts is increased by only one even for a value recalled from a memory or the like. In the case where a complicated expression is calculated by using a memory, only one recalled value is counted even if a plurality of additions and subtractions are performed for the memory. Therefore, the number of actual calculations and the number indicated by the counter are not identical with each other.
Japanese Laid-Open Patent Publication Nos. 57-150056 and 02-15359 disclose a calculator for comparing a plurality of displayed values. Therefore, there is a problem in that a user should compare the result of a calculation with a comparison value.
Since there is no state display showing that the calculation state is now in the course of input of a numeral unit or after the input of an operator, the user forgets the element being input. Therefore, If the user seeks for the element being input based on the value of the counter, the user cannot see with which part the input should be started.